Would the John McCains of the world back Hillary over Rand Paul in ’16?

Yesterday, I noted Sen. John McCain’s recent comments, where he lamented: “There are times these days when I feel that I have more in common on foreign policy with President Obama than I do with some in my own party.”

Today, my bloggingheads colleague Bill Scher ups the ante, positing the theory that a Rand Paul nomination for president might cause the McCains of the world to jump on the Hillary bandwagon.

Where might the “new Republican internationalists” go if Paul wins this intra-party battle? Considering that likely Democratic nominee Hillary Clinton helped engineer the U.N.-backed military coalition that ousted Libyan dictator Moammar Gadhafi, and reportedly pushed Obama to directly arm the Syrian resistance, it’s not hard to envision a “Republicans for Hillary” campaign if the alternative is Rand Paul.

As I have long noted, the conservative coalition is in danger of coming apart at the seams. But Scher cautions that — even if this plausible, though unlikely, scenario were to play out — it still wouldn’t necessarily imply a long-term political reordering:

The 1972 “Democrats for Nixon” effort helped sink Sen. George McGovern, but it did not doom the Democratic Party. George Romney’s prediction that the 1964 nomination of Barry Goldwater spelled the “suicidal destruction of the Republican Party” did not prove prophetic either.

Even the rift caused by Teddy Roosevelt’s walkout from the 1912 Republican convention to form a new Progressive Party was healed four years later. Roosevelt, itching to enter World War I, was determined to defeat Woodrow Wilson (then running for re-election on the slogan “He Kept Us Out Of War”) and was willing to overlook the isolationism that remained among Republicans. Often, a common enemy forces factions to paper over differences.

But sometimes the differences are too great. The last major party to collapse was the Whigs, formed in 1834 to oppose the policies of Democratic President Andrew Jackson. But by the 1850s, the issue of slavery was unavoidable and the Whigs fatally split.

If McCain were to jump ship and endorse a candidate from the other party (as his friend and former 2000 Democratic vice presidential nominee, Joe Lieberman did when he endorsed McCain in 2008), it would be a big deal. McCain was, after all, the 2008 nominee.

But the larger problem would be that McCain might represent a larger bloc of neoconservatives and internationalists who make up a sizable portion of the Republican coalition — especially at the opinion leader level.

Of course, even if Paul were to win the nomination, this theory assumes he wouldn’t make efforts to build bridges or balance the ticket. The younger Paul (who just endorsed Mitch McConnell for re-election) has proven rather adept at politics.